Ocean Bottom

_{-- O c e a n b o t t o m --} _{click on the question number for the answer}
Q 1.
	How was the vertical cliff on Bay Shore Drive formed?
Q 2.
	What type of rock lies under the peat soil of the Everglades National Park?
Q 3.
	Is it reasonable to expect that fish would inhabit a man-made reef to a degree which would appreciably affect sport fishing?
Q 4.
	Our anglers club, of which I am a director, hopes to obtain permission from the U.S. Corps of Engineers to construct an artificial reef for offshore fishing. It will lie in about 70 feet of water, approximately one and one-half miles offshore and be built of rock and non-metallic scrap. Our question is, in what direction should the reef lie? The general direction of the shore is east to west and the tide flows from the east. Should the reef be built in an east-west direction parallel to the beach, or should it be constructed from north to south, perpendicular to these factors?
Q 5.
	I read somewhere that South America was once connected to Africa and, in fact, that all continents were once joined in a great super continent. What do marine scientists think about this?
Q 6.
	We are trying to achieve safe boat docking at Lake Shastina and Lake Tahoe, Nevada, where the waves sometimes become 6 to 10 feet high. Local health agencies will not permit any more breakwaters, but will allow some type of clean wave-breaker. Can you give us a solution?
Q 7.
	Can you please tell me if the Bahama Islands and Grand Bahama Bank were formed geologically in the same way as the State of Florida by the lifting up of the continental shelf?
Q 8.
	I am a rock and fossil collector, and recently found marine fossils in a gravel pit about 5 miles west of LaBelle, Florida, on Route 80. Can you tell me how long ago this area was covered by Gulf waters, and how old these marine fossils are?
Q 9.
	Two friends and I have begun a small private project along the coast near here. We have built a small reef constituted of one car body and several ex-commercial washing machines. We hope to make it the first of several such reefs, especially since it seems to have been very successful so far. In the two months since we constructed it, there has been a remarkable influx of local sea life. However, before we go any further, we would like to obtain some information regarding the results of similar tests in other areas. We hope to use other materials in the next reef in order to determine the preference of the new inhabitants for one material over another. I am trying to maintain a proper journal of the proceedings to facilitate comparison, but having little idea of how experts would do it makes it difficult. Are there any good up-to-date publications available on comparative artificial reef projects? Sorry to bother you again, but the other day I injected a kelp crab with formalin and it promptly shed several of its legs. Is this a reaction to poison or a defense against attack from natural enemies?
Q 10.
	On a recent trip to the British West Indies, we became interested in the geologic origin of the Cayman Islands. Are they of volcanic or coral origin?
Q 11.
	Can you provide information on the geological development of the islands comprising the outer rim of the Cay Sal Bank, as compared to that of the Florida Keys and the Bahamas?
Q 12.
	Are the most ancient rocks on earth found in either the Appalachians or in eastern Canada?
Q 13.
	The members of my diving club would like to establish an artificial reef, using a Liberty ship. Can you tell us how to go about it?
Q 14.
	Would sulfur compounds leaching from artificial reefs made of tires have any adverse effects on the spawning of reef fishes?
Q 15.
	What is the best procedure to use when anchoring on an artificial reef?
Q 16.
	We recently photographed the freighter Stavronikita, which lies at a depth of 100 to 130 feet about 1/4 mile off the west coast of Barbados. Can you provide historical information about this ship?
Q 17.
	What is the origin of the Baths, a formation of huge, rounded boulders piled one on the other on the southwestern coast of Virgin Gorda in the British Virgin Islands?
Q 18.
	On the island of Curacao, Netherlands Antilles, there are hills with coral rock deposits that must be hundreds of feet high. Could you please tell me their approximate age and if the sea actually was high enough to cover them at one time?
Q 19.
	Can you provide information on the uses and construction of stationary artificial islands?
Q 20.
	I coordinate a group of wildlife protection volunteers, and we are interested in building artificial reefs off southern Brazil. Where can we obtain information about different types of artificial reefs and their success in creating new “life islands”?
Q 21.
	How are the various types of natural islands formed? Also, are they all formed in the same way?
Q 22.
	How do scientists determine the age of rocks?
Q 23.
	How far is it possible to drill into the earth for core samples? Is it possible to reach the asthenosphere?
Q 24.
	I understand that the Bahama banks, over which numerous small islands are scattered, are limestone. Under all that limestone, is the rock oceanic or continental?
Q 25.
	I am an experienced diver who wants to help researchers by collecting data at offshore artificial reefs. How do I get started?
Q 26.
	Is this the Japanese land-reclamation project similar to the one carried out in the Netherlands?


_{-- a n s w e r s a b o u t t h e O c e a n b o t t o m --}
	Q&A 1.	How was the vertical cliff on Bay Shore Drive formed? Miami, Florida
	The notches near the base of the cliff at several points are characteristic of wave erosion of a rocky shore. This indicates that the sea level once stood at about the base of the cliff. From evidence elsewhere in the world this higher level of the sea is believed to have occurred some 6000 years ago.
go back to Questions
	Q&A 2.	What type of rock lies under the peat soil of the Everglades National Park? Ft. Lauderdale, Florida
	Much of the Everglades National Park is floored by a limestone which geologists call the Miami Oolite. The term oolita is from the Greek word for egg, "oos" and refers to the minute egg-shaped grains of which this entire layer of rock is formed. The history of this rock goes back some thirty to fifty thousand years ago when south Florida was a shallow submarine bank. Some of the sediments deposited in that sea have become the limestones which form the arc-shaped oolite ridge between Ft. Lauderdale and Coot Bay. The individual particles, called ooliths, are similar in size and shape to sand grains. A section of these particles examined under the microscope shows that each individual grain consists of a series of concentric shells, like the layers of an onion, formed around a central sand grain or shell fragment. Each layer was laid down by precipitation of calcium carbonate from seawater in the same fashion as well water in limestone country forms a limy scale in ea kettles or water pipes. Present day examples of this process occur on shallow banks in the Gulf of Suez and on the Bahama Banks where the water is unusually hot and salty. Important changes in sea level have occurred since the deposition of the Miami oolite sediments and when sea level stood at least twenty feet below its present level, the rainwater falling on the surface of this sediment first dissolved the limestone particles and then as it percolated down through the rock the calcium carbonate was precipitated between the grains to form a coherent rock.
go back to Questions
	Q&A 3.	Is it reasonable to expect that fish would inhabit a man-made reef to a degree which would appreciably affect sport fishing? Ft. Lauderdale, Florida
	There is no doubt that artificial reefs increase the amount of cover available to fishes and that in the long run the results are a greater survival of the young and a larger total number of fishes in the area. This has been clearly demonstrated in Texas and Alabama where the extensive stretches of sandy bottom are found, and where fishing once was restricted to a very few rocky areas. The introduction of artificial reefs here has been very successful in terms of improving angler catch.
go back to Questions
	Q&A 4.	Our anglers club, of which I am a director, hopes to obtain permission from the U.S. Corps of Engineers to construct an artificial reef for offshore fishing. It will lie in about 70 feet of water, approximately one and one-half miles offshore and be built of rock and non-metallic scrap. Our question is, in what direction should the reef lie? The general direction of the shore is east to west and the tide flows from the east. Should the reef be built in an east-west direction parallel to the beach, or should it be constructed from north to south, perpendicular to these factors? New York, New York
	It is difficult to recommend the proper alignment of the reef without knowing the currents, the prevailing seas and the amount of current scouring and sand transport that is apt to occur in your particular region. Soft sand under your reef might be eroded away by strong currents thus sinking your entire structure. If the current are strong and you suspect that sand scouring would be a factor, you would be advised to place the structure parallel to the current. This would probably cause deepening of the area along the upstream and lateral portions of the reef site, which would be desirable up to a certain point. Additional information can be had by writing to the Sport Fishing Institute, Bond Building, Washington 5, D.C.
go back to Questions
	Q&A 5.	I read somewhere that South America was once connected to Africa and, in fact, that all continents were once joined in a great super continent. What do marine scientists think about this? Miami, Florida
	The theory of drifting continents, first proposed in the nineteenth century is still hotly debated today. A map of the earth shows that South America would fit against Africa with remarkable snugness, and most other land masses could be fitted into place to complete a giant jigsaw puzzle continent. The hypothesis is further substantiated by studies of magnetism in rocks, which suggest that continents have swung around from earlier positions. Articles on this subject will appear in future issues of Sea Frontiers.
go back to Questions
	Q&A 6.	We are trying to achieve safe boat docking at Lake Shastina and Lake Tahoe, Nevada, where the waves sometimes become 6 to 10 feet high. Local health agencies will not permit any more breakwaters, but will allow some type of clean wave-breaker. Can you give us a solution? Orinda, California
	Without details of the health agency's restrictions, it is difficult to envision the best solution to your breakwater problem. It would appear, however, that three possibilities are available: a submerged breakwater, a floating breakwater, or a conventional surface-piercing breakwater with openings near the bottom to permit circulation. Which of these you might select would depend on the local conditions. In any case, we suggest that you hire an engineer who specializes in this type of work to advise you.
go back to Questions
	Q&A 7.	Can you please tell me if the Bahama Islands and Grand Bahama Bank were formed geologically in the same way as the State of Florida by the lifting up of the continental shelf? Orange City, Florida
	Florida and the Bahamas were formed in a similar way giologically, but not by the lifting up of the continental shelf. Instead, the shelf area sank slowly and offshore an island area also sank. While the bases of the areas were sinking or slowly being pulled down by forces deep in the earth, their tops were collecting sediments at a rapid rate, thereby keeping the surfaces of the land close to the surface of the sea. The sediments were mainly the shells and coral skeletons that make up coral reefs. This growth of sediments kept up with the sinking of the original land, so that now, over 250 million years later, an oil well drilled to the extraordinary depth of 14,200 feet on Andros Island did not get through the pile of ancient shell and coral (now solid limestone). Florida today has more land area than the Bahama Banks because it has received more sediment and/or sank more slowly over the last few geologic ages. When the sea level rose again as a result of the last great glaciers about 15,000 years ago, it came up and flooded the Bahama Banks, so that they are about 8 to 10 feet deep on the average between the islands. The Florida peninsular was only partially covered by the rising sea.
go back to Questions
	Q&A 8.	I am a rock and fossil collector, and recently found marine fossils in a gravel pit about 5 miles west of LaBelle, Florida, on Route 80. Can you tell me how long ago this area was covered by Gulf waters, and how old these marine fossils are? Round Lake Heights, Illinois
	It is difficult to provide definite information about your fossils without seeing them. It can be said, however, that your fossils probably came from the Tamiami Formation, which is generally considered Miocene in age (about 10,000,000 years old). The area was last covered by the sea during the Pleistocene (Ice Age), 1000,000 to 200,000 years age.
go back to Questions
	Q&A 9.	Two friends and I have begun a small private project along the coast near here. We have built a small reef constituted of one car body and several ex-commercial washing machines. We hope to make it the first of several such reefs, especially since it seems to have been very successful so far. In the two months since we constructed it, there has been a remarkable influx of local sea life. However, before we go any further, we would like to obtain some information regarding the results of similar tests in other areas. We hope to use other materials in the next reef in order to determine the preference of the new inhabitants for one material over another. I am trying to maintain a proper journal of the proceedings to facilitate comparison, but having little idea of how experts would do it makes it difficult. Are there any good up-to-date publications available on comparative artificial reef projects? Sorry to bother you again, but the other day I injected a kelp crab with formalin and it promptly shed several of its legs. Is this a reaction to poison or a defense against attack from natural enemies? Canada
	Some publications currently available which will contain useful information on locations, types, materials, markers, cost, and government requirements for artificial reefs are: (1) "Housing Scheme for Fishes," Sea Frontiers, Vol. 8, No. 2, May 1962; (2) "Artificial Reefs," Publication 4-E American Littoral Society, Highlands, N.J. 07732; (3) "Artificial Reefs as Tools of Sport Fishery Management in Coastal Marine Waters," Bulletin No. 1700, Sport Fishing Institute, 719 13th Street, N.W., Washington, D.C. 20005; (4) "Artificial Fishing Reefs in Florida," Florida Board of Conservation. Drawer F, St. Petersburg, Florida 33731.
go back to Questions
	Q&A 10.	On a recent trip to the British West Indies, we became interested in the geologic origin of the Cayman Islands. Are they of volcanic or coral origin? Atlanta, Georgia
	All three of the Cayman Islands (Grand Cayman, Little Cayman, and Cayman Brac) are composed of two different limestones. The Bluff Limestone, a dense fine-grained type of rock approximately 30 million years old (Middle Tertiary), comprises the core of each of the islands. Around their present shorelines, the Bluff Limestone is covered by the Ironshore Formation, another limestone unit about 1 million years old (Pleistocene). The limestone corrodes under the action of rainwater and decaying plant matter to produce a rough, pitted and peaked topography called "microkarst." (See " The Ironshore," Sea Frontiers, Vol. 12, No. 6, November-December, 1966). The limestone is only partly coral in origin. Many other animals and plants, especially calcareous algae, help to produce the lime, mud and sand that harden to form the limestone of tropical islands in the Bahamas and Caribbean.
go back to Questions
	Q&A 11.	Can you provide information on the geological development of the islands comprising the outer rim of the Cay Sal Bank, as compared to that of the Florida Keys and the Bahamas? Marathon, Florida
	Cay Sal Bank, like Great and Little Bahama Banks, is a steep-sided plateau rising from several thousand feet of water, upon which carbonate sediment is presently accumulating and has been accumulating for over 100 million years. Cay Sal is similar in its general morphology to the atolls of the South Pacific, having a shallow raised "rim" (which occasionally breaks the surface as islands or cays), and a deeper bowl-shaped center. Many carbonate geologists do not classify Cay Sal Bank as a true Pacific-type atoll, however, because it lacks massive fringing reefs and does not rise from oceanic depths. Two excellent references on the geological history of the Florida Keys/Bahamas area are "Miami Limestone of Florida and its Recent Bahamian Counterpart" by J.E. Hoffmeister, K.W. Stockman, and H.G. Multer (Bulletin of the Geological Society of America, 78: 175-190) and "Geology and Origin of the Florida Keys" by J.E. Hoffmeister and H.G. Multer (Bullentin of the Geological Society of America, 79: 1487-1502).
go back to Questions
	Q&A 12.	Are the most ancient rocks on earth found in either the Appalachians or in eastern Canada? Miami, Florida
	The oldest rocks found on earth to date were discovered in western Greenland at the mouth of a fjord, Ameralik, not far from the capital (Godthab). These rocks have been determined to be approximately 3.9 billion years old. They were discovered in 1966 by Bic McGregor, a New Zealander working for the Greenland Geological Survey. In contrast, the Appalachian belt is very young-a mere 350 million years old. Northeastern Canada, however, does contain some very old rocks dating as far back as 2.8 billion years.
go back to Questions
	Q&A 13.	The members of my diving club would like to establish an artificial reef, using a Liberty ship. Can you tell us how to go about it? Jupiter, Florida
	Applications for use of obsolete Liberty ships as artificial reefs are handled by the United Stated Maritime Administration, Fleet Disposal Branch, 14th and E Streets, N.W., Washington, D.C. 20230. As of May, 1977, however, a total of 29 such ships had been reassigned to various states for this purpose, and there were only six ships still available. Information on how to acquire permits and build reefs with Liberty ships may be obtained from Dr. Richard Stone, Atlantic Estuarine Fisheries Service, Beaufort, North Carolina 28516 and by reference to Report MASGP-77-002, empirical and Theoretical Observations on the Potential Economic Benefits and Costs Associated with Mississippi/ Alabama Liberty Ship Reef Programs, available from the Sea Grant Consortium, Shearwater Drive, Ocean Springs, Mississippi 39564.
go back to Questions
	Q&A 14.	Would sulfur compounds leaching from artificial reefs made of tires have any adverse effects on the spawning of reef fishes? Huron, Ohio
	Very little is known about the leaching of sulfur compounds from rubber in seawater, but, thus far, fishes living on artificial reefs made of tires have shown no adverse effects. This may be due to colonization of the tire surfaces by bacteria, algae, sponges, hydroids, and bryozoans. These organisms rapidly produce a thick encrustation that inhibits an interchange between the rubber and the seawater, thus slowing the leaching process.
go back to Questions
	Q&A 15.	What is the best procedure to use when anchoring on an artificial reef? Palm Beach, Florida
	It is best to drop the anchor well upwind or upcurrent of the selected fishing location; then let out the anchor line until the boat is directly over the reef, according to Saltwater Conservation, 1979(6). To avoid losing the anchor, a special reef anchor may be constructed by bending two 4-foot sections of 3/8-inch concrete-reinforcing rods double and then sliding a 12-inch section of 1 1/2 -inch or larger pipe over the bent rods. Next, bend the ends of the rods to from a grapple, and fill the pope section with concrete. This anchor will hold most boats in position once it snags on an old tire or some wreckage, and will usually loosen easily when a strong pull is made on the anchor line and the grapple straightens.
go back to Questions
	Q&A 16.	We recently photographed the freighter Stavronikita, which lies at a depth of 100 to 130 feet about 1/4 mile off the west coast of Barbados. Can you provide historical information about this ship? Point Pleasant, New Jersey
	The former 356-foot steel Greek freighter Stavronikita was sunk by a United States Navy demolition crew on November 22, 1978 off Barbados to create an artificial reef. The 22-year-old vessel, owned by Delax Shipping Line, Ltd., had lost her usefulness as a freighter following a disaster while she was enroute from Ireland to Barbados with a cargo of cement. On August 26, 1976, at about 6 a.m. fire broke out amidships, followed by an explosion that killed 6 of the 30 persons aboard. The fire destroyed all of Stavronikita's communications systems, so her Master had the crew paint SOS in huge letters port and starboard. As a result, the stricken freighter was spotted and taken in tow four days later by the Danish ship Benny Skou about 200 miles off Guadeloupe. On August 31, she finally arrived at Carlisle Bay, Barbados. In October 1977, Stavronikita was purchased at a public auction for $30,000 by the Barbados Parks and Beaches Commission. A year later, after the oil was removed from here bunkers and the tanks cleaned with a special detergent, the freighter was ready for sinking and her new role as a sanctuary for marine life.
go back to Questions
	Q&A 17.	What is the origin of the Baths, a formation of huge, rounded boulders piled one on the other on the southwestern coast of Virgin Gorda in the British Virgin Islands? St. Clair Shores, Michigan
	The Baths are composed of a type of granite called granodiorite, which formed millions of years ago as a shallow intrusion possibly several kilometers below the surface of the earth, according to Dr. Thomas W. Donnelly of the State University of New York at Binghamton. Long after solidification, the granodiorite was exposed by tectonic uplift and erosional removal of overlying rock. All granites fracture as they cool, and exhumed granite consists of fracture-bounded blocks. Commonly, such fractures are only a few feet apart. At southwestern Virgin Gorda, however, the fractures are spaced wider, and this, in combination with the even texture and lack of grain of the granodiorite, has resulted in truly huge structures. These blocks weather most readily at corners and edges because of exposure, gradually becoming more rounded. As they weather, some blocks lean on others. The result: the Baths, with their idyllic inner pools of crystalline water. Granodiorite is relatively uncommon in the West Indies and usually outcrops in a less spectacular fashion; therefore, the Baths are considered unusual.
go back to Questions
	Q&A 18.	On the island of Curacao, Netherlands Antilles, there are hills with coral rock deposits that must be hundreds of feet high. Could you please tell me their approximate age and if the sea actually was high enough to cover them at one time? Croton, New York
	There are two kinds of hills on Curacau - those made up of coral reef limestone, and those made up of igneous rocks, according to Dr. Duncan F. Sibley of Michigan State University. In the vicinity of Willemstad, the hills are composed of consolidated coral reef sediments deposited about 4 million years ago when that area was underwater. In the intervening years, due to world-wide fluctuations in sea level, these hills have been exposed and inundated by the ocean several times. Additionally, there has been a small amount of tectonic uplift of the area. In Neogene and Quaternary Geology of Aruba, Curacao, and Bonaire (Publication 78, Foundation for Scientific Research in Surinam and the Netherlands Antilles, 293 pages, March 1974). P.H. de Buisonje estimates that since the earliest coral limestone formations were deposited, the total change in relative height of sea level has been approximately 600 feet. Most of the inland hills in the northern part of Curacao are composed of igneous rocks formed more than 100 million years ago, and they have also been inundated many times since then.
go back to Questions
	Q&A 19.	Can you provide information on the uses and construction of stationary artificial islands? Somerset, New Jersey
	Most fixed artificial islands are used as oil/gas drilling and production platforms and offshore ports. Fixed islands constructed of dredged material or cement provide stability against ice encroachment and extremely heavy seas in harsh environments such as the Beaufort and North seas. Many are built by piling up dredged material to create a sea mountain that extends above the water surface. Sandbags and filter cloths are placed on the slopes to combat erosion. Another type utilizes a large caisson, which is floated to the drilling location, lowered to the sea floor by water ballast, and filled with dredged material. Islands are also created in frozen nearshore waters of the Beaufort Sea by cutting huge holes in the ice and filling them with gravel. In the North Sea, oil explorers use gigantic concrete platforms, called gravity structures because they are anchored by their own massive weight. In less harsh environments, such as off the coast of California and in the Gulf of Mexico, numerous steel rigs anchored to the sea floor with piling are used for oil/gas recovery. New designs include compliant structures, such as guyed towers and tension-leg platforms, which deflect under the action of environmental forces. Artificial islands are also constructed to provide more land space for human habitation and airports in overpopulated areas. In the Netherlands, dredge-material islands are used as dams against disastrous floods. One of these islands is being used as the construction site for the 131-foot-high concrete piers that will form a modern storm-surge barrier with movable flood gates for the Osterschelde. Off Landskrona, Sweden, an artificial island is being created with the disposal of gypsum, a by-product from the manufacture of phosphoric acid. The area was dredged, drained, diked, and divided into four polyethylene-lined pools. The gypsum slurry is pumped into the pools, and water is drawn off. The pools will be filled in about ten years, and the island will be transformed into a grassy recreation area.
go back to Questions
	Q&A 20.	I coordinate a group of wildlife protection volunteers, and we are interested in building artificial reefs off southern Brazil. Where can we obtain information about different types of artificial reefs and their success in creating new “life islands”? Porto Alegre, Brazil
	Artificial reefs are composed of various types of waste materials, including concrete rubble, quarry rock, automobile bodies, tires, liberty ships, old plumbing fixtures, and even solid blocks of coal combustion waste from power plants. Prefabricated fish houses have also been built out of concrete and fiberglass. Placed on barren bottoms, they attract and concentrate fishes and other marine life. The June-July 1982 issue of Marine Fisheries Review is devoted to the subject of artificial reefs and marine fisheries enhancement. A copy of this issue (vol. 44, no. 6-7) may be obtained at a cost of $3.25 ($4.10 foreign) from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. In addition, the following publications are available from the Sea Grant Advisory Program, G022 McCarty Hall, University of Florida, Gainesville, Florida 32611: SGR-41, Artificial Reefs, Conference Proceedings 1979 ($3.00); MAFS-9, Constructing an Artificial Reef Buoy (free of charge); and MAFS-20, Artificial Reef Site Selection and Evaluation (free). Sea Frontiers articles on this subject have included: “Artificial Reefs off California: An Update,” vol. 28, no. 6; “Liberty-Ship Reefs in the Gulf of Mexico,” vol. 26, no. 2; and “Artificial Reefs,” vol. 20, no. 1.
go back to Questions
	Q&A 21.	How are the various types of natural islands formed? Also, are they all formed in the same way? Victoria, British Columbia
	Most islands can be grouped into three structural categories: barrier islands, volcanic islands, and coral islands. Other types can be formed from glacial deposits located offshore on the continental shelf, and by the rooting of mangrove trees in shallow water. Barrier islands are narrow strips of unconsolidated sand that lie parallel to shore. The regular actions of waves, as well as storm seas, continually reshapes and moves these islands. A variety of mechanisms can initiate the formation of barrier islands. Sand spits, created by the transport of sand around headlands and across bay mouths, are often breached by the ocean to form islands. The tops of ancient dunes drowned by rising sea level can also constitute initial barrier island structures. Volcanic islands are composed of accumulations of lava and volcanic ash. They are formed along the edges of the large plates of crustal material that compose the outermost layer of earth. The plates slowly “grow” outward from the spreading zones along one margin, and, hence collide with other plates along the opposite margin. These areas of spreading and collision are characterized by a high rate of volcanic activity. When these boundaries occur under the sea, islands are formed. Hot spots beneath the plates also create island/seamount chains that are often in the center of oceanic plates. Volcanic islands composed primarily of ash will be quickly eroded and disappear below the sea; however, islands with an outer coat of lava will remain. Coral islands were originally submerged reefs at a time when sea level was higher. As sea level fell and the reefs were exposed, islands formed.
go back to Questions
	Q&A 22.	How do scientists determine the age of rocks? Jerusalem, Israel
	The principal means of dating rocks used the decay of radioisotopes as a clock. For any given isotope of a radioactive element, the rate of radioactive decay is constant. By determining the proportion of a radioactive isotope that has decayed, scientists can calculate the time elapsed since the rock was formed. As there are several different radioactive elements that can serve as clocks, several types of rocks can be ages using these techniques. Rocks are also dated using the assumption that in layered rocks the lower layers are older. Rocks positively dated using radioisotope clocks are used to calibrate the dates of other rock layers above or below them, which cannot be dated directly. Within sequences of layered sedimentary rocks, different microscopic fossils are found. After years of study, scientists have been able to associate certain specific fossils with particular time periods. For example, on a large scale, rocks containing dinosaur fossils are between 65 and 215 million years old. Specific dinosaurs lived only during known time periods, so rocks with specific dinosaur fossils can be dated rather precisely in this way. On a much finer scale, microscopic fossil animal and plant communities found in sedimentary rocks can be used to date ocean sediments.
go back to Questions
	Q&A 23.	How far is it possible to drill into the earth for core samples? Is it possible to reach the asthenosphere? Riverside, California
	To date, the deepest hole drilled for core samples is the Kola borehole, which is now 12 kilometer (7.4 miles) deep on the Kola Peninsula in the Soviet Union. While there are-or are plans for-ultradeep holes in the United States, Great Britain, and Germany, the Russians are the world’s experts at deep drilling. As yet, however, no borehole is even close to penetrating the rigid lithosphere, which includes the crust and upper mantle. The asthenosphere lies below the lithosphere. It begins at about 50 to 100 kilometers (30 to 62 miles) below the earth’s surface and continues to about 500 to 700 kilometers (310 to 430 miles). The high pressures and temperatures deep within the crust are destructive to drilling equipment. Scientists estimate that, with current technology, it should be possible to drill to a maximum depth of about 15 kilometers (9.3 miles). Costs of deep drilling are also high; it is estimated that the Russians have spent $150,000,000 on the Kola borehole. Current plans for ultradeep boreholes do not include attempts to reach the mantle. The top layer of the mantle is believed to be highly mineralized and is considered by drillers to be a “hostile environment,” with temperatures greater than 1000°C (1832°F) and pressures of 100,000 atmospheres.
go back to Questions
	Q&A 24.	I understand that the Bahama banks, over which numerous small islands are scattered, are limestone. Under all that limestone, is the rock oceanic or continental? Chicago, Illinois
	The answer is not yet known. The only way to get an answer is to drill through the limestone banks down into the rock below. The limestone, or calcium carbonate, banks are believed to be several miles thick. When, and if, a deep-enough hole is drilled, cores will reveal whether the underlying rock is a basalt characteristic of oceanic crust or if it is a granite characteristic of continental crust. At least two theories have been proposed for the origin of the rock under the Bahama banks, or platform. Both theories have the following features in common. The rock foundation under the banks originally must have been near the water surface. Calcium carbonate corals, algae, and sediments accumulated in the shallow water, forming a limestone cap on the underlying rock. As the rock foundation sank, or subsided, its limestone cap grew upward so that the top of the cap was maintained near the sea surface, forming the banks. One theory also suggests that the rock under the Bahama banks is ocean floor. The continents of Africa and the Americas were once joined. They began to rift apart about 230 million years ago during the Triassic period, forming what was to become the Atlantic Ocean. Initially, this new sea was small and shallow. As the Atlantic Ocean continued to widen, the basin became deeper. The other theory suggests that rock broke off from the American and/or African continents when they rifted apart. Initially, the rock was at sea level which allowed limestone to accumulate. Again, the rock foundation subsided under the weight of the growing limestone.
go back to Questions
	Q&A 25.	I am an experienced diver who wants to help researchers by collecting data at offshore artificial reefs. How do I get started? Stuart, Florida
	Guidelines for sport divers who wish to document and store data gathered at artificial reeks appear in Artificial Reef Research Diver’s Handbook, edited by J. Halusky. The 198-page book is available for $5 from Florida Sea Grant, Building 803, University of Florida, Gainesville, FL 32611-0341.
go back to Questions
	Q&A 26.	Is this the Japanese land-reclamation project similar to the one carried out in the Netherlands? Huntsville, Alabama
	No. Japan’s project involves carrying land into the sea, and the Netherlands project involved pumping the sea off the land. “They differ as much from each other as a Japanese pagoda differs from a Dutch windmill!” says Henk Meijer in Geographical, March 1993. In Japan’s Kobe Bay, the first stage of Port Island, completed in 1981, provided 1,077 acres of land area. The Port Island extension, scheduled for completion in 1996, will provide an additional 960 acres. Two other Kobe Bay islands under construction will support new airports: the one south of Port Island for domestic flights, and the other one further south in the bay for international flights. Engineers excavate stone and earth from the Rokko Mountains and dump them into the shallow bay until the amount of land needed for a project rises well above sea level. Stage one of Port Island, for example, required about 100 million cubic yards of fill material. The excavated mountain areas now are being transformed into residential and industrial sites. Using a nearly opposite reclamation, the Ditch pumped water out of the sea to increase the land area of the Netherlands. To establish a polder – a tract of reclaimed land – engineers circled an area with a dike, dug drainage canals, and built pumping stations. Pumps emptied water out of the polder area but most operate continuously to keep the new land dry. In four polders, the Dutch have reclaimed from the sea about 407,500 acres of land, much of which they use for agriculture.
go back to Questions


	Rosenstiel School of Marine & Atmospheric Science Library University of Miami, FL USA 4600 Rickenbacker Causeway, Miami, Florida 33149 Phone: 305 421 4060 Fax: 305 421 9306 E-mail: libcirc@rsmas.miami.edu		go to the top